Thin display devices, mounted at electronic devices such as portable telephones, digital cameras and PDAs, are utilized in a wide range of applications. At a display device equipped with a nematic liquid crystal element, an image formed at the transmission-type liquid crystal element in which the transmittance is controlled for each pixel becomes visible as the liquid crystal element is illuminated from the rear. Since the liquid crystal element itself does not emit light, the display device requires an illuminating member (e.g., a backlight) for illuminating the liquid crystal element. There is also a display device known in the related art that includes an organic EL (electroluminescence) element that emits light in place of a liquid crystal element and thus does not require a backlight member. Structures that may be adopted in such liquid crystal display devices and organic EL display devices are disclosed in, for instance, patent reference 1 and patent reference 2.
In addition, there are display devices achieved by using cholesteric liquid crystals and PN (polymer network) liquid crystals, which are utilized in so-called electronic paper or an Electronic Book (registered trademark) (see, for instance, patent reference 3 and patent reference 4). Such a display device, in which ambient light is used as illuminating light, adopts a structure that allows individual pixels constituting the liquid crystal element to be switched to a transmitting state or a reflecting state. The ambient light is reflected and diffused at a pixel switched to the reflecting state and shows up as a white glow at, for instance, a PN liquid crystal, whereas the ambient light is transmitted through a pixel switched to the transmitting state. If the liquid crystal element includes an absorbing layer such as a black layer for absorbing the ambient light disposed under the liquid crystal, this pixel is visually recognized as a black area. Since no light is emitted, this type of display device does not need to consume a great deal of power.    Patent reference 1: Japanese Laid Open Patent Publication No. 2004-125962    Patent reference 2: Japanese Laid Open Patent Publication No. 2004-127662    Patent reference 3: Japanese Laid Open Patent Publication No. 2003-140114    Patent reference 4: Japanese Laid Open Patent Publication No. 2003-98541